Air conditioning apparatus currently in use on many aircraft incorporate machines that include a turbine and compressor mounted on the same shaft, with air supplied to the compressor from the engine. The air supplied from the engine (engine bleed air) is typically cooled by passing it through a heat exchanger which uses ram air to remove the heat from the bleed air. That cooled air then enters the compressor, where it is pressurized to a higher level. That high pressure air is then typically cooled as it passes through a second heat exchanger which also utilizes ram air to remove the heat of compression. The cooled high pressure air then enters the turbine, where it expands while performing work that powers the compressor rotor. As it expands and performs work, the temperature of the air is reduced and that cooled air is supplied to the cabin. Numerous variations on this basic configuration have been proposed, as evidenced by U.S. Pat. Nos. 4,261,416; 5,025,642, and 6,796,131. The basic principle for these systems is also well known and such systems are described in general as air cycle systems.
The basic principle associated with all air cycle systems is that when a turbine performs work, it expends energy and as the energy is expended, the temperature of the air cools as it expands through the turbine. The difference in temperature between the inlet and the outlet increases as the difference in pressure between the inlet and outlet of the turbine increases. Consequently, more cooling occurs when the pressure difference across the turbine increases. If the outlet of the turbine can be depressed below ambient pressure, the pressure difference across the turbine will increase, and correspondingly a lower exhaust temperature will result. Based on those principles, a depressed ambient system whereby the inlet of the compressor draws air below ambient, creating a vacuum, will result in greater cooling of the air as it passes through the turbine. Unfortunately, past air conditioning systems have not utilized this potential as does the present air conditioning apparatus invention which uses a unique turbine, heat exchanger and compressor configuration. This unique turbine, heat exchanger and compressor configuration offers numerous advantages over previous air conditioning systems including increased cooling, increased efficiency, increased reliability as well as simplified construction and the important ability to operate in an aircraft without the need for supplied power.